Piezo-Electric Shear Rheometry: Further developments in experimental implementation and data extraction

TL;DR

This paper advances the Piezo-electric Shear Gauge technique by optimizing data extraction for higher frequencies and simplifying the measuring cell, improving measurements of viscous liquids near their glass transition.

Contribution

The paper introduces a simplified PSG design and an optimized data extraction method, extending frequency range and enhancing measurement accuracy for viscous liquids.

Findings

Extended frequency range to 50-70 kHz.

Simplified the measuring cell with one piezo-electric disc.

Identified the need for a soft spacer to accommodate thermal contraction.

Abstract

The Piezo-electric Shear Gauge (PSG) [Christensen & Olsen, Rev. Sci. Instrum. 66, 5019, 1995] is a rheometric technique developed to measure the complex shear modulus of viscous liquids near their glass transition temperature. We report recent advances to the PSG technique: 1) The data extraction procedure is optimized which extends the upper limit of the frequency range of the method to between 50 and 70 kHz. 2) The measuring cell is simplified to use only one piezo-electric ceramic disc instead of three. We present an implementation of this design intended for liquid samples. Data obtained with this design revealed that a soft extra spacer is necessary to allow for thermal contraction of the sample in the axial direction. Model calculations show that flow in the radial direction is hindered by the confined geometry of the cell when the liquid becomes viscous upon cooling. The method is especially well-suited for -- but not limited to -- glassy materials.